Description

These macros classify character-coded integer values. Each is a predicate returning non-zero for true, 0 for false. The behavior of these macros, except isascii(), is affected by the current locale (see setlocale(3C)). To modify the behavior, change the LC_TYPE category in setlocale(), that is, setlocale(LC_CTYPE, newlocale).
In the “C” locale, or in a locale where character type information is not defined, characters are classified according to the rules of the US-ASCII 7-bit coded character set.

The isascii() macro is defined on all integer values. The rest are defined only where the argument is an int, the value of which is representable as an unsigned char, or EOF, which is defined by the <stdio.h> header and represents end-of-file.

Functions exist for all the macros defined below. To get the function form, the macro name must be undefined (for example, #undef isdigit).

For macros described with Default and Standard conforming versions, standard-conforming behavior is provided for standard-conforming applications (see standards
(5)) and for applications that define __XPG4_CHAR_CLASS__ before including <ctype.h>.

Default

isalpha()

Tests for any character for which isupper() or islower() is true.

Standard conforming

isalpha()

Tests for any character for which isupper() or islower() is true, or any character that is one of the current locale-defined set of characters for which none of iscntrl(),
isdigit(), ispunct(), or isspace() is true. In “C” locale, isalpha() returns true only for the characters for which isupper() or islower() is true.

isalnum()

Tests for any character for which isalpha() or isdigit() is true (letter or digit).

isascii()

Tests for any ASCII character, code between 0 and 0177 inclusive.

isblank()

Tests whether c is a character of class blank in the current locale. This macro/function is not available to applications conforming to standards prior to SUSv3. See standards(5)

iscntrl()

Tests for any ``control character'' as defined by the character set.

isdigit()

Tests for any decimal-digit character.

Default

isgraph()

Tests for any character for which ispunct(), isupper(), islower(), and isdigit() is true.

Standard conforming

isgraph()

Tests for any character for which isalnum() and ispunct() are true, or any character in the current locale-defined “graph” class which is neither a space (“ ”)
nor a character for which iscntrl() is true.

islower()

Tests for any character that is a lower-case letter or is one of the current locale-defined set of characters for which none of iscntrl(), isdigit(), ispunct(), isspace
(), or isupper() is true. In the “C” locale, islower() returns true only for the characters defined as lower-case ASCII characters.

Default

isprint()

Tests for any character for which ispunct(), isupper(), islower(), isdigit(), and the space character (“ ”) is true.

Standard conforming

isprint()

Tests for any character for which iscntrl() is false, and isalnum(), isgraph(), ispunct(), the space character (“ ”), and the
characters in the current locale-defined “print” class are true.

ispunct()

Tests for any printing character which is neither a space (“ ”) nor a character for which isalnum() or iscntrl() is true.

isspace()

Tests for any space, tab, carriage-return, newline, vertical-tab or form-feed (standard white-space characters) or for one of the current locale-defined set of characters for which isalnum() is false. In the “C”
locale, isspace() returns true only for the standard white-space characters.

isupper()

Tests for any character that is an upper-case letter or is one of the current locale-defined set of characters for which none of iscntrl(), isdigit(), ispunct(), isspace
(), or islower() is true. In the “C” locale, isupper() returns true only for the characters defined as upper-case ASCII characters.

Default

isxdigit()

Tests for any hexadecimal-digit character ([0−9], [A−F], or [a−f]).

Standard conforming

isxdigit()

Tests for any hexadecimal-digit character ([0−9], [A−F], or [a−f] or the current locale-defined sets of characters representing the hexadecimal digits
10 to 15 inclusive). In the “C” locale, only

0 1 2 3 4 5 6 7 8 9 A B C D E F a b c d e f

are included.

Return Values

If the argument to any of the character handling macros is not in the domain of the function, the result is undefined. Otherwise, the macro or function returns non-zero if the classification is TRUE and 0 if the classification is FALSE.

Usage

These macros or functions can be used safely in multithreaded applications, as long as setlocale(3C) is not being called to change the locale.